The invention relates to a data carrier having an electrical circuit with the help of which indication means are implemented that are arranged to indicate a change of a parameter influencing the data carrier in relation to a threshold value of the parameter, which threshold value divides a first parameter range from a second parameter range.
The invention further relates to a circuit for a data carrier with the help of which indication means are implemented that are arranged to indicate a change of a parameter influencing the data carrier in relation to a threshold value of the parameter, which threshold value divides a first parameter range from a second parameter range.
The invention further relates to a method of determination for determining the occurrence of a change of a parameter influencing a data carrier, the occurrence of the change of the parameter being determined in relation to a threshold value of the parameter, which threshold value divides a first parameter range from a second parameter range.
A data carrier of the kind defined in the first paragraph, a circuit of the kind defined in the second paragraph, and a method of determination of the kind defined in the third paragraph are known from patent WO 99/53279.
The known data carrier is in the form of a passive data carrier, is suitable for detecting a change in the ambient temperature of the data carrier in relation to a temperature threshold, is intended for use in a vehicle tire, and has indication means that are implemented in the form of a mechanical maximum temperature measuring switch that forms a sensing means for sensing the ambient temperature. In essence, the maximum temperature measuring switch comprises two bars that slightly overlap one another in an overlapping region and that do not touch one another at a starting temperature. Each of the bars has a laminated structure comprising a layer of metal and a plurality of mutually differing layers of silicon. The laminated structure causes the two bars to bend in the same direction by virtue of the bimetallic effect if there is a change in temperature, with the first barxe2x80x94due to the fact that it is differently sized from the second barxe2x80x94undergoing less bending than the second bar. Hence, beginning from the starting temperature, the second bar bends relative to the first bar when there is a rise in temperature until it touches the first bar on one side of the latter. As the temperature continues to rise up to the threshold temperature value, the two bars slide against one another in the overlapping region. When the threshold temperature value is exceeded, the two bars lose physical contact with one another andxe2x80x94due to the removal of the force exerted on the first bar by the second barxe2x80x94the first bar springs back substantially to its starting position. In this state the two bars differ appreciably from one another in the bending they show and, similarly to the situation that exists at the starting temperature, are not in physical contact with one another. Only if the ambient temperature falls back to the starting temperature is the bending of the second bar reduced sufficiently for it eventually to touch the first bar at a point of contact. In this situation, the maximum temperature measuring switch forms an electrically conductive, closed contact, which closed contact can be detected by means of an electrical circuit belonging to the data carrier. Hence it is only at this starting temperature that the maximum temperature measuring switch is controlled to its active state and is thus suitable for determining the fact that there has, at least once in the past, been a change in the ambient temperature of the data carrier in relation to the temperature threshold. This characteristic of the maximum temperature measuring switch is not critical especially if, following a temperature change of this kind occurring for the first time, the starting temperature obtains again at the time when the temperature change is determined to have occurred by means of a communication station provided and arranged to cooperate with the known data carrier.
In connection with a bimetallic sensor of the kind described above, reference may be made, for example, to U.S. Pat. No. 5,712,609. Reference should be made in this connection to FIGS. 1A to 1D, 2A to 2D, and 3 and the related passages in the description. This reference to the patent in question is deemed to incorporate the disclosure thereof in the present document by reference.
There is a problem with the known data carrier in that, if the ambient temperature is higher than the threshold temperature value and the passive data carrier is fed with power at this time, it cannot be clearly determined with the maximum temperature measuring switchxe2x80x94due to the fact that this can only be done intermittently as a function of ambient temperaturexe2x80x94whether there was a temperature change of this kind in the past, given that the two bars are not in contact with one another when the starting temperature exists, both before any such temperature change occurred for the first time and after a temperature change of this kind. This fact may well not be critical where the application is to a vehicle tire, because a vehicle tire is virtually always able to cool down to its starting temperature after a run during which a temperature change of this kind may possibly have occurred. In other cases however, the fact described above may have disadvantageous consequences.
It is an object of the invention to overcome the problems outlined above in a data carrier of the kind defined in the first paragraph above and in a circuit of the kind defined in the second paragraph above and in a method of determination of the kind defined the third paragraph above, and to provide an improved data carrier and an improved circuit and an improved method of determination.
To achieve the object detailed above, in accordance with the invention, provision is made, in a data carrier of the kind defined in the first paragraph above, provision is made for the indication means to be arranged so as to give a permanent indication of the change of the parameter during the time following the occurrence of the change for the first time.
To achieve the object detailed above, in accordance with the invention, provision is made, in a circuit of the kind defined in the second paragraph above for the indication means to be arranged so as to give a permanent indication of the change of the parameter during the time following the occurrence of the change for the first time.
To achieve the object detailed above, in accordance with the invention, provision is made in a method of determination of the kind defined in the third paragraph above for the determination of the occurrence of the change of the parameter to be permanent during the time following the occurrence of the change for the first time.
The provisions according to the invention provide the advantage that, regardless of a parameter that exists momentarily and influences the data carrier, a permanent indication of high reliability can be obtained of a change of the parameter that has already occurred earlier, and as a result the occurrence of this change can be determined. This is of advantage principally if the parameter is formed by the ambient temperature and if the data carrier is used with a deep-frozen foodstuff to determine that there has been, in the past, an unwanted break in the deep-freezing. In connection with the determination of a break in the effect of deep-freezing on a foodstuff, or in other words when determining the occurrence of a change in temperature in relation to a defrosting point of the foodstuff that forms a threshold temperature value, it is possible to avoid deleterious effects on the health of human beings by means of the provisions according to the invention, because people can be prevented from eating a foodstuff of this kind that may possibly have already been defrosted once in the past and have then been deep-frozen again.
In a solution according to the invention, it has also proved advantageous if the sensing means are arranged to remain in the changed detecting state, irrespective of the ambient temperature, during the time following the occurrence of the change of the parameter for the first time. This gives the advantage that, with mechanical sensor means arranged to sense ambient temperature, such as, for example, by means of a sensor that employs the bimetallic effect and is arranged to implement the provisions according to the invention, it is possible to obtain a permanent indication of a change in temperature during the time following the occurrence of the change in temperature for the first time.
In a solution according to the invention, it has also proved advantageous if at least one conductor region is provided to determine the occurrence of the change of the parameter and if at least one storage means is provided that is arranged to store a medium suitable for influencing an impedance, which medium can be dispensed from the storage means towards at least one conductor region, and if recognition means are provided for recognizing a state of the impedance that exists in the at least one conductor region and that depends on the presence or absence of said medium. This gives the advantage that the permanent indication of the change of a parameter can be obtained on the basis of physics-related or chemical properties of the medium virtually irrespective of mechanical influencing factors. Also, a solution of this kind can be manufactured in a structurally simple manner.
In a solution according to the invention, it has also proved advantageous if feed means are provided for feeding the medium to the at least one conductor region. This gives the advantage of providing an assurance that the medium, which may, for example, be in the liquid state, will be fed as accurately as possible to the at least one conductor region.
In a solution according to the invention, it has also proved advantageous if activation means are provided that are arranged to activate the feed of the medium to the at least one conductor region. This gives the advantage that the activation of the feed of the medium to the at least one conductor region can be carried out after the manufacture of a data carrier on the premises of a data carrier manufacturer or on the premises of a user of the data carrier. It may be mentioned in this connection that the activation means may be formed, for example, by the application of a pressure to the data carrier to activate the feed of the medium, such as happens, for example, when the data carrier is applied to a product by pressure. This gives the advantage that, as a consequence of the application, it can be clearly determined at a time following the application that there was, at the time of application, a minimum pressure that is required for the safe and reliable application of the data carrier to the product. What has proved particularly advantageous, however, is for the activation means to be arranged to automatically activate the feed of the medium, which is in its frozen, i.e. solid, state, as a result of a change in the ambient temperature of the data carrier in relation to a freezing point of the medium such as occurs, for example, when a foodstuff to which the data carrier is applied is cryogenically frozen, which means that after the medium has changed from its solid to its liquid state there are no problems in feeding it from the storage means to the at least one conductor region.
In a solution according to the invention, the at least one conductor region may be arranged inside the data carrier adjacent the electrical circuit. It may be mentioned in this connection that the at least one conductor region may, for example, be arranged on a supporting foil carrying the data carrier, on which foil a communications coil intended for communications and the electrical circuit connected to the communications coil are arranged in a known fashion in the case of an active or a passive data carrier. In such a case the at least one conductor region is connected to the electrical circuit by connecting means. It has proved particularly advantageous, however, for the at least one conductor region to be a part of the electrical circuit. This gives the advantage that no additional stages of production are required to provide the at least one conductor region when manufacturing the data carrier, and that the at least one conductor region is in a clearly defined location relative to the electrical circuit. Another advantage is that, in a process for manufacturing the electrical circuit, the manufacture of the at least one conductor region can be carried out as part of the process, thus affording a considerable saving in costs when manufacturing the electrical circuit and hence also the data carrier. It may also be mentioned in connection with the at least one conductor region that the at least one conductor region may be covered with a layer for passivating the electrical circuit, thus reliably preventing any possible oxidation of the at least one conductor region subsequent to the manufacture of the electrical circuit. What has proved particularly advantageous, however, when using inert materials for the at least one conductor region is for the at least one conductor region to be formed as part of the electrical circuit free of the passivating layer. A gold coating of the at least one conductor region may, for example, be mentioned in this connection. This gives the advantage that a change in resistance can be recognized between, for example, two conductor regions for the purpose of an uninterrupted determination of the occurrence of the change of the parameter for the first time, which recognition may most easily be carried out electrically.
In a solution according to the invention, the storage means may be in sponge form, in which case an outer side of a means of this kind in sponge form must have closed pores to prevent any unwanted and uncontrolled emergence of the medium from the storage means in sponge form. The provision of storage means in sponge form gives the advantage that they can be brought virtually directly into contact with the at least one conductor region without the need to call on additional means. Another advantage is that storage means of this kind may be given an initial shape, which has proved particularly advantageous when assembling the data carrier. It has, however, proved particularly advantageous for the storage means to be given the shape of a bladder. This provides the advantage that the storage means can be manufactured as inexpensively as possible. It also gives the advantage that the shape of the storage means can be distorted virtually without any mechanical resistance being encountered. This gives the further advantage that a storage means of this kind in bladder form can be incorporated in the data carrier with relatively few problems when the data carrier is being manufactured. It this connection it has also been found particularly advantageous for the storage means in bladder form to be produced from an elastic material that exerts an initial pressure on the medium stored either as a result of the storage means being filled with the medium or as a result of the storage means being fitted into the data carrier. This gives the advantage that, as a function of orientation and position, it encourages a desired emergence of the medium from the at least one storage means in the direction of the at least one conductor region.
In a solution according to the invention, the feed means may be in sponge, or non-woven, or tube, or hose form. What has proved particularly advantageous, however, is for the feed means to be in capillary form. This gives the advantage of ensuring that the medium is fed to the at least one conductor region reliably and virtually irrespective of the orientation or position of the data carrier by making use of the physical principle of capillary attraction.
In a solution according to the invention, the recognition means may be arranged so as to recognize inductively a state of the impedance that is present in the at least one conductor region and that depends on the presence or absence of the medium. It may be mentioned in connection with the recognition means arranged for inductive recognition that they may be arranged so as to recognize an inductance of a coil or a quality (Q factor) of the coil, which coil may be implemented by means of the single conductor region. In a solution according to the invention, the recognition means may be arranged for the capacitive recognition of a state of the impedance that is present in the at least one conductor region and that depends on the presence or absence of the medium. It may be mentioned in this connection that the recognition means arranged for capacitive recognition may, for example, be constructed as a non-stable multivibrator in which the frequency of a recognition signal can be changed as a function of the presence or absence of the medium, for example, between two conductor regions. What has provided particularly advantageous, however, is for the recognition means to be formed by a comparator stage. This gives the advantage that where there are at least two conductor regions free of the layer for passivating the electrical circuit, the recognition of a level of resistance between the two conductor regions can be carried out in a manner that is as simple as possible to implement electronically.
In a solution according to the invention, the medium may be prepared in the form of alcohol diluted with water. What has proved particularly advantageous, however, is for the medium to be produced in the form of an aqueous salt solution. This gives the advantage that a salt solution of this kind has particularly good electrical conductivity, which has proved particularly advantageous in connection with recognition means arranged to recognize a resistance between, for example, two conductor regions, which regions may, for example, be coated with platinum to prevent oxidation. It may also be mentioned here that the electrical conductivity may be advantageously acted on by, for example, adding metallic components such as powdered metal or metal ions, for example, or graphite. It may further be mentioned that the medium provided may be a so-called two-component liquid in which the two components are separate from one another in their solid state but which, after the two components have melted and mixed together, will no longer freeze. This gives the advantage that, when the medium is present between the conductor regions, an impedance that is not dependent on the ambient temperature can be recognized between the two conductor regions by the recognition means. It may also be mentioned it connection with the two-component liquid that the at least one storage means may advantageously be arranged to store the two components of the liquid separately. It may further be mentioned that the medium may alternatively be formed by organic liquids or jelly-like substances or gaseous substances or powder-like substances, in which cases an absence or presence of the given medium must be recognizable at the at least one conductor region on the basic of the physics-related or chemical properties of the media. It may further be mentioned that use may also be made as a medium of solidified liquids that can be fed to the at least one conductor region in their liquid state as a result of a change in temperature.